Groot was originally written as an extra-terrestrial, tree-like being who came to Earth intending to capture human beings for experimentation. He appeared later in The Incredible Hulk Annual #5 in 1976 where he fought and lost to the Hulk.
In 2006, he was rewritten as a hero and was included in Annihilation: Conquest and Annihilation: Conquest – Star-Lord where he sacrificed himself multiple times for the good of the team. Ultimately, Rocket Raccoon was able to salvage a cutting of Groot and regrow him.
Groot’s powers include the ability to rebuild himself, even from small fragments, he can manipulate trees, and he appears to be resistant to fire. Though his speech is limited (“I AM GROOT”), Groot is highly intelligent and it is believed that even though he can only speak a few words in English, he is actually communicating much more than that.
Groot is Rocket Raccoon’s best friend.